Nissan Repair: 1988 Nissan Sentra 1.67 bucking, thump thump thump, fuel pressure regulator

Question
I have an intermitant "bucking" problem with a 1988 Nissan Sentra 1.67 automatic. Seems to happen most when it's hot and/or after the engine gets hot. Yet, it doesn't happen everyday. This morning, started up OK, drove 8 miles no problem. Shut it off for about 20 minutes and it's bucking again.It's almost like when giving gas it starts to run on 3 cylinders. In nuetral the engine "rolls" like a diesel, thump, thump, thump, duhh, thump, thump, thump, duhh. I have to feather the gas pedal to keep it runing, have to keep one foot on the brake, at a higher rpm than I like, to put it in gear, or it will stall. When it comes time for it to go into second gear it starts "bucking" have to feather the gas pedal so it will shift. The same for secord to third gear, "bucking" have to feather, play with the gas pedal, back off, give a little until it shifts gears. Give too much gas and the "bucking" starts. Can't get it to go over 43 miles an hour to shift to next gear. If I push gas pedal to floor, seems like it cuts out altogether. Was even driving down the interstate doing about 65 mph, then suddenly, no power. Pulled off the interstate and the darrump, darrump, darrump, like it's only firing on three cylinders. I've read every question and your answers to them and: I've checked the distributer as you directed, ran a q-tip came out completely dry. Mechanic, for $345, replaced the fuel pump; mechanic checked with EGR vacuum line disconnected still have same problem; replaced all the vacuum hoses. Mechanic "now" thinks it's the fuel pressure regulator (another costly guess). Another guess (mine) could it be the fuel cut off solenoid? My biggest problem: I don't have the money to put into this car on guesses, and don't have the money to buy another car. One more thing, I don't know if it's a factor or not, the exhaust after the cat and before the muffler is nothing but holes, enough to sound like I'm running straight pipes and no muffler. Any direction you can offer will be greatly appreciated. Thank you in advance. Mike

Answer
Mike,

I know you say the distributor is dry but that would be my recommendation.  If the converter is blocked you can check it by doing a pressure check where the oxygen sensor is.  If the backpressure is over 3 pouinds replace the converter.  But, you could simply disconnect the exhaust before the converter and drive it.  But, for me I would replace the distributor.  Email me back and let me know what you find.